The research of the McArdle Laboratory for Cancer Research is divided into three broad categories: Biochemical Studies in Chemical Carcinogenesis, Molecular Biology and Genetics of Tumor Viruses, and Regulatory Mechanisms in Tumor Biology. The chemical carcinogenesis program encompasses a broad fundamental approach to the chemistry, biochemistry, and biology of tumor initiation and promotion by chemicals. The overall objective of these studies is a detailed knowledge of chemical carcinogenesis that will facilitate the identification of the stages at which controls can be imposed on the process. The studies in tumor virology have as their overall objective a broad understanding of the molecular biology and genetics of the oncogenic retro-, papova-, and herpes-viruses. The ultimate goal of these studies is the elucidation of the features that determine the oncogenicity of these viruses and the mechanisms by which they cause transformation. Of special interest are the essential features of the DNA genomes of these viruses, genetic factors that influence the expression of the viral oncogenes, and control of transcription of the viral genomes. The tumor biology program is a multidisciplinary approach to regulatory mechanisms that influence the growth, replication, and differentiation of normal and cancer cells. The approaches include studies of DNA and chromatin replication, transcription of DNA, the processing of nuclear RNA, the stability of mRNA and its transport to the cytoplasm, the mechanisms of differentiation of phage and of various cell types, and the immunogenetics of transplantation antigens of the mouse.